1. Field of the Invention
The present invention relates to a driving-side pulley that is one component of a belt-type continuously variable transmission transmitting a rotational power from a driving shaft to a driven shaft while continuously varying a speed of the rotational power that has been transmitted in accordance with a change of a rotational speed of the driving shaft.
2. Related Art
There has been previously proposed a belt-type continuously variable transmission including a driving-side pulley supported by a driving shaft, a driven-side pulley supported by a driven shaft, a V-belt wounded between both the pulleys, and transmitting a rotational power from the driving shaft to the driven shaft while continuously varying a speed of the rotational power, which has been transmitted to the driven shaft, in accordance with a rotational speed of the driving shaft.
To explain in detail, the driving-side pulley includes a fixed sheave supported by the driving shaft in an immovable manner along an axis line of the driving shaft and in a non-rotatable manner around the axis line with respect thereto, a movable sheave supported by the driving shaft in a movable manner along the axis line of the driving shaft and in a non-rotatable manner around the axis line with respect thereto, a return spring pressing the movable sheave in a direction away from the fixed sheave, and a flyweight mechanism.
The flyweight mechanism presses the movable sheave in a direction toward the fixed sheave against a pressing force of the return spring with utilizing a centrifugal force that has a value corresponding to the rotational speed of the driving shaft.
Meanwhile, the belt-type continuously variable transmission is required to perform a belt clutch function when an engine is in an idle state and is also required to perform an engine braking function when a vehicle travels. The belt clutch function is a function that interrupts or reduces the power transmission from the driving shaft to the driven shaft so as to effectively prevent a creep phenomenon when the engine is in the idle state.
In order to achieve the two requirements, Japanese patent No. 2620490 discloses a driving-side pulley (hereinafter referred to as a first conventional configuration) including a fixed pulley immovable in the axis line of the driving shaft, a movable sheave movable in the axis line of the driving shaft, a one-way clutch that is interposed between the driving shaft and the fixed sheave and allows a power transmission only from the fixed sheave to the driving shaft while preventing a power transmission in a reverse direction, a return spring pressing the movable sheave in a direction away from the fixed sheave, a flyweight mechanism that presses the movable sheave in a direction toward the fixed sheave against a pressing force of the return spring with utilizing a centrifugal force that has a value corresponding to the rotational speed of the driving shaft, an auxiliary spring generating a force for pressing the movable sheave to one side surface of the belt in cooperation with the flyweight mechanism, and an engagement mechanism connecting the driving shaft and the fixed sheave with each other in a non-rotatable manner around the axis line as the movable sheave moves in a direction toward the fixed sheave by a predetermined distance.
In the first conventional configuration, when the engine is in an idle state, although the belt is brought into a tension state by pressing the movable sheave by the flyweight mechanism and the auxiliary spring, the rotational power is not transmitted from the driving shaft to the fixed sheave since the engagement mechanism is in a non-engagement state. Specifically, in this condition, the power transmission from the driving shaft to the belt is performed only via the movable sheave so that a torque of the rotational power that is transmitted from the driving shaft to the driven shaft is reduced, whereby the creep phenomenon can be prevented.
On the other hand, if the rotational speed of the driven shaft becomes higher than that of the driving shaft when the vehicle travels, the rotational power from the driven shaft is transmitted to the driving shaft from the belt via movable sheave as well as via the one-way clutch and the fixed sheave, whereby the engine braking function can be effectively performed.
However, the first conventional configuration has a problem in that the engine braking function cannot be sufficiently performed in a case where an operator releases an engine output operating member such as an accelerator pedal when the vehicle travels.
To explain in detail, if the engine output operating member is released when the vehicle travels, the belt moves inward in a radial direction with respect to the driving-side pulley and comes into contact with a bottom surface of a V-shaped groove of the driving-side pulley.
The fixed sheave that engages with one side surface (a first side surface) of the belt is immovable in the axis line direction. On the other hand, the movable sheave that engages with the other side surface (a second side surface) of the belt is subjected to the force generated by the flyweight mechanism when the engine is in an idle state and the force generated by the auxiliary spring, both the forces pressing the movable sheave in a direction toward the fixed sheave. However, the movable sheave is also subjected to the force generated by the return spring so as to press the movable sheave in a direction away from the fixed sheave.
More specifically, the movable sheave is pressed toward the fixed sheave only by a force obtained by subtracting the force generated by the return spring from a resultant force of the force generated by the flyweight mechanism and the force generated by the auxiliary spring.
That is, in the first conventional configuration, when the engine output operating member is released during traveling of the vehicle, the power transmission is mainly performed only through a path or a route extending from the inner circumferential surface of the belt to the bottom surface of the V-shaped groove. Therefore, enough frictional force cannot be obtained between the belt and the movable sheave and between the belt and the fixed sheave. As a result, the belt slips with respect to both the sheaves so that the engine braking function cannot be effectively performed.
In order to achieve the above-mentioned two requirements, Japanese patent No. 3524533 discloses a driving-side pulley (hereinafter referred to as a second conventional configuration) including a fixed pulley that is immovable in the axis line and non-rotatable with respect to the driving shaft, a movable sheave that is movable in the axis line and non-rotatable with respect to the driving shaft, a return spring pressing the movable sheave in a direction away from the fixed sheave, a flyweight mechanism that presses the movable sheave in a direction toward the fixed sheave against a pressing force of the return spring with utilizing a centrifugal force that has a value corresponding to the rotational speed of the driving shaft, a collar that is inserted around the driving shaft so as to be rotatable with respect to both the sheaves and form the bottom surface of the V-shaped groove by its outer circumferential surface, and a one-way clutch that is interposed between the driving shaft and the collar so as to allow a power transmission only from the collar to the driving shaft while preventing a power transmission in a reverse direction, wherein the collar is provided with a conical surface coming into contact with a first side surface of the belt that is positioned on a side near the fixed sheave when the belt is moved onto the bottom surface of the V-shaped groove.
In the second conventional configuration, when the engine is in an idle state, the belt is positioned so that the first side surface comes into contact with the conical surface of the collar and the inner circumferential surface comes into contact with the outer circumferential surface of the collar while a second side surface coming into contact with the movable sheave. As explained earlier, the power transmission from the driving shaft to the collar is interrupted by the one-way clutch. Accordingly, the power transmission from the driving shaft to the belt is performed only via the movable sheave so that a torque of the rotational power that is transmitted from the driving shaft to the driven shaft is reduced, whereby the creep phenomenon can be prevented.
On the other hand, if the rotational speed of the driven shaft becomes higher than that of the driving shaft when the vehicle travels, the rotational power from the driven shaft is transmitted to the driving shaft from the belt via movable sheave as well as via the collar and the one-way clutch, whereby the engine braking function can be effectively performed.
However, as with the first conventional configuration, the second conventional configuration has a problem in that the engine braking function cannot be sufficiently performed in a case where an operator releases the engine output operating member when the vehicle travels.
To explain in detail, if the engine output operating member is released when the vehicle travels, the belt moves inward in a radial direction with respect to the driving-side pulley and comes into contact with the bottom surface of the V-shaped groove of the driving-side pulley.
The collar that engages with the first side surface of the belt is immovable in the axis line direction. On the other hand, although the movable sheave that engages with the second side surface of the belt is subjected to the force generated by the flyweight mechanism so as to press the movable sheave in a direction toward the fixed sheave, the movable sheave is also subjected to the force generated by the return spring so as to press the movable sheave in a direction away from the fixed sheave.
More specifically, the movable sheave is pressed toward the fixed sheave only by a force obtained by subtracting the force generated by the return spring from the force generated by the flyweight mechanism when the engine in the idle state.
That is, as in the first conventional configuration, in the second conventional configuration, the power transmission is mainly performed only through a path or a route extending from the inner circumferential surface of the belt to the bottom surface of the V-shaped groove when the engine output operating member is released during traveling of the vehicle. Therefore, enough frictional force cannot be obtained between the belt and the collar and between the belt and the movable sheave. As a result, the belt slips with respect to the collar and the movable sheave so that the engine braking function cannot be effectively performed.